This invention relates generally to electrical discharge machining and more particularly to electrical discharge machining workpieces, such as aircraft engine parts, which have several features machined therein.
Electrical discharge machining (EDM) is a well known process for forming features, such as holes, slots and notches of various shapes and configurations, in an electrically conductive workpiece. Conventional EDM apparatuses typically employ an electrode having the desired shape that is advanced toward the workpiece. A suitable power supply is applied to create an electrical potential between the workpiece and electrode for forming a controlled spark which melts and vaporizes the workpiece material to form the desired feature. The cutting pattern of the electrode is usually computer numerically controlled whereby servomotors control the relative positions of the electrode and workpiece. During machining, the electrode and workpiece are immersed in a dielectric fluid, which provides insulation against premature spark discharge, cools the machined area, and flushes away the removed material.
One drawback to electrical discharge machining is that it is a relatively slow process, especially when several distinct features need to be machined into a workpiece. This is particularly so in the aircraft engine industry where electrical discharge machining is widely used for machining various features into aircraft engine parts. To increase the manufacturing output of such parts, it is common to use an EDM apparatus that machines a number of parts at one time. Such an apparatus has a plurality of work stations, each of which has a workpiece fixture located in a single dielectric tank. The work stations are all typically connected to a common power supply. Thus, machining takes place in series one part at a time. That is, a spark will be created in the first work station and then the next work station and so on until each station has a spark supplied. This sequence is repeated until the machining operation is completed for each workpiece. Although throughput can be improved with this type of apparatus, machining multiple features into a single workpiece is still a relatively slow process.
To further speed production, it has been proposed to use an EDM apparatus that employs multiple electrodes in each work station. Such an EDM apparatus is capable of performing multiple machining operations on a workpiece simultaneously. However, a separate servomotor, power supply and computer numerical control (CNC) is provided for each electrode. The large number of servomotors, power supplies and CNCs increases the complexity and cost of the manufacturing system and requires a lot of floor space in the machining shop. The total number of power supplies and CNCs can be reduced by using a power transfer switch that selectively delivers power to one work station at a time. While reducing the number of power supplies and CNCs, this configuration still utilizes a large number of servomotors. Such EDM apparatuses can be susceptible to manufacturing interrupts.
Accordingly, there is a need for an EDM apparatus that provides multiple machining operations with less EDM equipment than is presently used and is less susceptible to manufacturing interrupts.
The above-mentioned need is met by the present invention which provides an electrical discharge machining apparatus including at least two work stations. A first servomotor is mounted above the first and second work stations, and a second servomotor mounted to the first servomotor so as to be selectively positioned over either of the first or second work stations by the first servomotor. The second servomotor is capable of causing relative motion between an electrode and a workpiece fixture in the first work station when positioned over the first work station and causing relative motion between an electrode and a workpiece fixture in the second work station when positioned over the second work station.
The present invention and its advantages over the prior art will become apparent upon reading the following detailed description and the appended claims with reference to the accompanying drawings.